Semiconductor light emission system

ABSTRACT

A semiconductor light emission system, comprising a semiconductor laser part constituted of a second conductive current restricting layer with a striped groove perforated therein, a first conductive clad layer, a first or second conductive active layer, a second conductive clad layer on a first conductive substrate, and a second conductive--first conductive-second conductive bipolar transistor part constituted of said second conductive current restricting layer, first conductive clade layer, first or second conductive active layer, second conductive active layer in a position other than the semiconductor laser part.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light emission system,and is particularly concerned with a semiconductor laser capable ofcontrolling a radiant power on a small current.

2. Description of the Prior Art

FIG. 7 is a characteristic curve representing one example of current vs.radiant power characteristic according to a conventional semiconductorlight emission system, and FIG. 8 is a sectional perspective diagramrepresenting a prior art semiconductor light emission system mentioned,for example, in Japanese Patent Laid-Open No. 192380/985.

In FIG. 7, the quadrature axis indicates an operating current, and theaxis of ordinate indicates a radiant power.

In FIG. 8, (1) denotes a first conductive (p-type or hereinafterreferred to as "p-") GaAs substrate, (2) denotes a p-Al₀.45 Ga₀.55 Asbuffer layer, (3) denotes a second conductive (n-type or hereinafterreferred to as "n-") GaAs current block layer which is a currentrestricting layer with a striped groove provided on the p-GaAs substrate(1), (4) denotes a p-Al₀.45 Ga₀.55 As lower clad layer, (5) denotes ap-type or n-type Al₀.15 Ga₀.85 As active layer, (6) denotes an n-Al₀.45Ga₀.55 As upper clad layer, (7) denotes an n-GaAs contact layer, (8)denotes a p side electrode, and (9) denotes an n side electrode.

A function of the prior art semiconductor light emission system will bedescribed with reference to FIG. 7 and FIG. 8.

When a positive voltage is impressed on the p side electrode (8) and anegative voltage on the n side electrode (9), a junction between then-GaAs block layer (3) and the p-Al₀.45 Ga₀.55 As lower clad layer (4)becomes inverted of bias in a domain where the n-GaAs block layer (3) ispresent between the electrodes (8), (9), therefore a current does notflow therein, and the current flows in concentration only on the openingof a striped groove (5a) or thereabout. In this case, a hole is injectedinto a portion near a bottom of the striped groove (5a) of the Al₀.15Ga₀.85 As active layer (5) from the p-Al₀.45 Ga₀.55 As lower clad layer(4), an electron is injected then from the n-Al₀.45 Ga₀.55 As upper cladlayer (6), and thus a light is emitted through a recombination of boththe two. According as a current level to be injected is further raised,an inductive emission begins presently, as shown in the characteristiccurve of FIG. 7, to lead to a laser oscillation. A threshold current forlaser oscillation will be 20 to 30 mA in the case of the semiconductorlight emission system of FIG. 8, and an operating current for obtaininga 3 mW radiant power is required at 40 mA or so.

The prior art semiconductor light emission system has theabove-described construction, and hence when a radiant power is to becontrolled, a laser driving current must be controlled direct, and sincethe driving current is large to run from several tens mA to severalhundreds mA, the problem is that a control circuit becomes inevitablycomplicated. Additional prior art is disclosed in the article entitled:"A Novel Self-Aligned Laser with Small Astigmatism Grown by MO-CVD" byY. Mihashi, Y. Nagai, H. Matsubara and K. Ikeda, which is shown onextended abstract of the 17th Conference on Solid State Devices andMaterials, Tokyo, pp. 63-66.

SUMMARY OF THE INVENTION

The invention has been done in view of the circumstances mentionedabove, and its object is to provide a semiconductor light emissionsystem capable of controlling a radiant power on a small current.

In order to attain the aforementioned object, the invention comprisesproviding a semiconductor laser part constituted of a second conductivecurrent restricting layer with a striped groove perforated therein, afirst conductive clad layer, a first or second conductive active layer,a second conductive clad layer on a first conductive substrate, and asecond conductive - first conductive - second conductive or firstconductive - second conductive first conductive bipolar transistor partin a position other than the semiconductor laser part.

The invention further comprises providing a semiconductor laser partconstituted of a first conductive clad layer, a first or secondconductive active layer, a second conductive first clad layer, a firstconductive current restricting layer with a striped groove perforatedtherein, a second conductive second clad layer on a first conductivesubstrate, and a first conductive - second conductive - first conductiveor second conductive - first conductive - second conductive bipolartransistor part constituted in a position other than the semiconductorlaser part.

In the bipolar transistor part according to the invention, an emittercurrent is controlled by the current injected into a base, a currentinjected into the semiconductor laser part is controlled consequently,and thus a radiant power is controlled thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view representing preferred embodiments (A)and (B) of a semiconductor light emission system according to theinvention;

FIG. 2 is a side sectional view representing embodiments (C) and (D) ofthe semiconductor light emission system of the invention;

FIG. 3 is a circuit diagram showing a simplified equivalent circuit ofthe embodiment (A) of FIG. 1 or the embodiment (D) of FIG. 2;

FIG. 4 is a circuit diagram showing a semiconductor light emissionsystem driving circuit when the system of FIG. 3 is used;

FIG. 5 is a circuit diagram showing a simplified equivalent circuit ofthe embodiment (B) of FIG. 1 or the embodiment (C) of FIG. 2;

FIG. 6 is a circuit diagram showing a semiconductor light emissionsystem driving circuit when the system of FIG. 5 is used;

FIG. 7 is a characteristic curve representing one example of current vs.radiant power characteristic according to a conventional semiconductorlight emission system;

FIG. 8 is a sectional perspective view showing an example of the priorart semiconductor light emission system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments (A) to (D) of the invention will now be described withreference to the accompanying drawings.

FIG. 1 to FIG. 6 are drawings representing the embodiments of theinvention, wherein FIG. 1 is a side sectional view representing theembodiments (A) and (B) of a semiconductor light emission system, FIG. 2is a side sectional view representing the embodiments. (C) and (D) ofthe semiconductor light emission system, FIG. 3 is a circuit diagramshowing a simplified equivalent circuit of the embodiment (A) of FIG. 1or the embodiment (D) of FIG. 2, FIG. 4 is a circuit diagram showing asemiconductor light emission system driving circuit when the system ofFIG. 3 is used, FIG. 5 is a circuit diagram showing a simplifiedequivalent circuit of the embodiment (B) of FIG. 1 or the embodiment (C)of FIG. 2, and FIG. 6 is a circuit diagram showing a semiconductor lightemission system driving circuit when the system of FIG. 5 is used.

In FIG. 1, (10) denotes an n-block layer electrode connected to then-GaAs block layer (3) working as a current restricting layer, (11)denotes a p-clad layer electrode connected to the p-AlGaAs lower cladlayer (4), (12) denotes a semiconductor laser part comprising the p-GaAssubstrate (1), the p-AlGaAs buffer layer (2), the n-GaAs block layer (3)working as a current restricting layer, the p-AlGaAs lower clad layer(4), the p- or n-type undoped AlGaAs active layer (5), the n-AlGaAsupper clad layer (6), and the n-GaAs contact layer (7), (13) denotes abipolar transistor part described hereinlater, (14) denotes a currentpath flowing into the semiconductor laser part (12) which will bedescribed hereinlater, (15) denotes a current path flowing into thebipolar transistor part (13) which will be described hereinlater, (T₁)denotes a terminal connected with the n side electrode (9), (T₂) denotesa terminal of the p-clad layer electrode (11), (T₃) denotes a terminalof the n-block layer electrode (10), and (T₄) denotes a terminalconnected with the p side electrode (8).

In FIG. 1, like reference characters represent like or correspondingcomponents in the aforementioned example, and hence a repeateddescription will be omitted.

In FIG. 2, (3a) denotes a p-GaAs block layer working as a currentrestricting layer with a striped groove provided thereon, (6a) denotes afirst n-AlGaAs upper clad layer as a first clad layer, (6b) denotes asecond n-AlGaAs upper clad layer as a second clad layer, (12) denotes asemiconductor laser part comprising the p-GaAs substrate (1), thep-AlGaAs lower clad layer (4), the p- or n-type undoped AlGaAs activelayer (5), the first n-AlGaAs upper clad layer (6a), the p-GaAs blocklayer (3a) as a current restricting layer, the second n-AlGaAs cladlayer (6b), and the n-GaAs contact layer (7), and (13) denotes a bipolartransistor part constructed as described hereinlater.

Then, in FIG. 1, the n-GaAs block layer (3) is formed between theundoped AlGaAs active layer (5) and the p-GaAs substrate (1), however,FIG. 2 indicates the construction wherein the p-GaAs block layer (3a) ispresent on the first n-AlGaAs upper clad layer (6a).

In FIG. 2 to FIG. 6, like reference characters represent like orcorresponding components in FIG. 1, and hence a repeated descriptionwill be omitted.

Next, the embodiments (A) to (D) will be described each with referenceto FIG. 1 to FIG. 6.

In the first place, the embodiment (A) will be taken up for descriptionwith reference to FIG. 1, FIG. 3 and FIG. 4.

The embodiment (A) comprises the semiconductor laser part (12) and thebipolar transistor part (13) of FIG. 1, the semiconductor laser part(12) being the same in construction as the semiconductor light emissionsystem in FIG. 8, and hence the repeated description will be omittedhere. The bipolar transistor part (13) comprises the undoped A(GaAsactive layer (5), the n-AlGaAs upper clad layer (6), the n-GaAs contactlayer (7) which is an emitter of the bipolar transistor part (13), the nside electrode (9) which is an emitter electrode of the transistor, thep-AlGaAs lower clad layer (4) which is a base of the transistor, thep-clad electrode (11) which is a base electrode of the transistor, then-GaAs block layer (3) which is a collector of the transistor, and then-block electrode (10) which is a collector electrode of the transistor,thus constituting the bipolar npn transistor (13).

Next, an operation of the embodiment (A) will be described according tothe drawing.

An operation of each of the layers (1) to (7) of the semiconductor laserpart (12) is equivalent to the above-described example, therefore thedescription will be omitted.

The bipolar transistor part (13) operates as an npn bipolar transistorof the emitter, the emitter electrode, the base, the base electrode, thecollector, and the collector electrode.

The operation will further be described with reference to the circuitdiagrams of FIG. 3 and FIG. 4.

As described above, an emitter corresponding domain in the bipolartransistor part (13) is common to the n-GaAs contact layer (7) and then-AlGaAs upper clad layer (6) of the semiconductor laser part (12),therefore a simplified equivalent circuit of the embodiment (A) will beas shown in FIG. 3, and the system of FIG. 3 will be realized as shownin FIG. 4 when connected through a circuit configuration.

In the circuit of FIG. 4, a steady-state current (I) by a constantcurrent source (16) flows between the terminal (T₁) and an earth (E).

Further, a controlling current (IB) by an alternating current signalsource (17) is injected in the p-AlGaAs lower clad layer (4) at aportion corresponding to the base of the bipolar transistor part (13).

In the circuit configuration of FIG. 4, the bipolar transistor part (13)is a common-collector transistor circuit, and a current I_(tr) flowingfrom the collector to the emitter can be controlled by a small change ofthe base current (IB).

The current I_(tr) corresponds to a current, in FIG. 1, injected fromthe n-block layer electrode (10) and flowing out to an external circuitby way of the n-block layer (3), the p-lower clad layer (4), the activelayer (5), the n-upper clad layer (6), the n-contact layer (7) and the nside electrode (9).

The current path is indicated by the path (15) of FIG. 1.

In the circuit shown in FIG. 4, a gross current (I) flowing to thesemiconductor laser part (12) or the system according to the inventionand to the bipolar transistor part (13) is constant, and the current (I)is expressed by the sum of a current (I_(LD)) flowing to thesemiconductor laser part (12) and a current (I_(tr)) flowing out of theemitter of the bipolar transistor part (13).

Accordingly, the current (I_(LD)) flowing to the semiconductor laserpart (12) (or the current flowing through the path (14) of FIG. 1) willbe:

    I.sub.LD =I-I.sub.tr =I-f(IB)                              (1)

Here, f(IB) represents a function of the current (IB). Generally, anoperating current of the laser and a radiant power are correlated asindicated in FIG. 7, and when the current exceeds a threshold necessaryfor oscillation, a relation between the radiant power and the currentbecomes almost linear.

Accordingly, the radiant power can be controlled by the small current(IB) injected from the p-clad layer electrode (11) corresponding to abase electrode from the aforementioned expression (1) in the system.

The embodiment (B) will be described next with reference to FIG. 1, FIG.5 and FIG. 6.

The embodiment (B) comprises the semiconductor laser part (12) and thebipolar transistor part (13) of FIG. 1, of which the semiconductor laserpart (12) is the same in construction as the embodiment (A) describedabove, and the description will be omitted consequently. In FIG. 1, thebipolar transistor part (13) constitutes a pnp bipolar transistor withthe p-AlGaAs lower clad layer (4) as a p-collector, the n-GaAs blocklayer (3) as an n-base, the p-AlGaAs buffer layer (2) and the p-GaAssubstrate (1) as a p-emitter.

In this case, a film thickness of each layer varies from theabove-described embodiment (A).

As mentioned hereinbefore, the p-emitter corresponding domain of thebipolar transistor (13) is common to the p-A(GaAs buffer layer (2) andthe p-GaAs substrate (1) of the semiconductor laser part (12), thereforea simplified equivalent circuit of the embodiment (B) will be as shownin FIG. 5.

A semiconductor light emission system driving circuit when theembodiment (B) shown in the circuit diagram of FIG. 5 is used is shownin FIG. 6.

An operation in this case may apply correspondingly to the embodiment(A) described hereinabove, therefore a repeated description will beomitted.

In the embodiment (B), the radiant power can also be controlled by asmall current injected from the n-block layer electrode (10)corresponding to a base electrode as in the case of embodiment (A).

The embodiment (C) will be described next with reference to FIG. 2, FIG.5 and FIG. 6.

The embodiment (C) comprises the semiconductor laser part (12) and thebipolar transistor part (13) of FIG. 2, of which the semiconductor laserpart (12) is constituted, as described in FIG. 2, of the p-GaAssubstrate (1), the p-AlGaAs lower clad layer (4), the AlGaAs activelayer (5), the first n-AlGaAs upper clad layer (6a), the p-GaAs blocklayer (3a), the second n-AlGaAs upper clad layer (6b), the n-GaAscontact layer (7), and the bipolar transistor part (13) is constitutedas a pnp bipolar transistor comprising the p-GaAs substrate (1), thep-AlGaAs lower clad layer (4), the undoped AlGaAs active layer (5), thefirst n-AlGaAs upper clad layer (6a) and the p-GaAs block layer (3a).

A simplified equivalent circuit of the embodiment (C) is equivalent toFIG. 5, and the semiconductor light emission system driving circuit isequivalent to FIG. 6.

Since an operation of the embodiment (C) applies correspondingly to theabove-described embodiment (A), no further description will be givenrepeatedly thereon.

In the embodiment (C), the radiant power can be controlled also by asmall current injected from the first n-upper clad layer electrode (10)corresponding to a base electrode as in the case of embodiment (A).

Next, the embodiment (D) will be described with reference to FIG. 2,FIG. 3 and FIG. 4.

The embodiment (D) comprises the semiconductor laser part (12) and thebipolar transistor part (13) of FIG. 2, of which the semiconductor laserpart (12) is similar to the semiconductor laser part (12) of theabove-described embodiment (C), therefore the description will beomitted. The bipolar transistor part (13) is constituted as an npnbipolar transistor comprising the first n-AlGaAs upper clad layer (6a),the p-GaAs block layer (3a), the second n-AlGaAs upper clad layer (6b)and the n-GaAs contact layer (7).

A simplified equivalent circuit of the embodiment (D) is equivalent toFIG. 3, and the semiconductor light emission system driving circuit issimilar to FIG. 4.

An operation of the embodiment (D) applies correspondingly to theembodiment (A) described hereinabove, therefore a repeated descriptionwill be omitted.

In the embodiment (D), the radiant power can also be controlled by asmall current injected from the p-block layer electrode (11)corresponding to a base electrode as in the case of embodiment (A).

Further, the embodiments (A) to (D) indicate the case where eachsemiconductor is formed of an AlGaAs group material, however, a similareffect will also be obtainable from forming of an InGaAs group material.

Then, each of the aforementioned embodiments has been described with thefirst conductive type as p-type and the second conductive type asn-type, however, a similar operating effect will be obtainable in asimilar construction from taking the first conductive type as n-type andthe second conductive type as p-type.

As described above, the invention comprises forming the bipolartransistor part of a current restricting layer, a clad layer and anactive layer in addition to the semiconductor laser part, therefore acurrent flowing to the semiconductor laser part can be controlled by thecurrent injected into a base of the bipolar transistor part, thusensuring an effect in controlling a radiant power on a small current.

What is claimed is:
 1. A semiconductor light emission system havinga) asemiconductor laser part including:(i) a p-side electrode, (ii) asubstrate, (iii) a buffer layer, (iv) a current block layer, (v) a lowerclad layer, (vi) an active layer, (vii) an upper clad layer, (viii) acontact layer, and (ix) an n-side electrode, and b) a bipolar npntransistor part constituted in a position other than said semi-conductorlaser part and including:(i) an emitter formed from said contact layer,(ii) a base formed from said lower clad layer, and (iii) a collectorformed from said current block layer.
 2. The device defined in claim 1,wherein said bi-polar npn transistor part includes:a) said active layer,b) said upper clad layer, c) said contact layer, d) said n-sideelectrode, e) said p-side electrode, f) said block layer; and g) ann-block electrode.
 3. The device defined in claim 1 and including:a) abase electrode connected to said lower clad layer, and b) a collectorelectrode connected to said current block layer.
 4. The device definedin claim 3 wherein the radiant power is controlled by a small currentinjected from said base electrode.
 5. The semi-conductor light emissionsystem as defined in claim 1, the semi-conductor being constituted of aAlGaAs material.
 6. The semi-conductor light emission system as definedin claim 1, the semi-conductor being constituted of a InGaAs material.7. A semi-conductor light emission system having:a) a semi-conductorlaser part including:(i) a p-side electrode, (ii) a substrate, (iii) abuffer layer (iv) a current block layer, (v) a lower clad layer, (vi) anactive layer, (vii) an upper clad layer, (viii) a contact layer, (ix) an-side electrode, and b) a bi-polar transistor part, constituted in aposition other than the semi-conductor laser part, and having:(i) acollector formed from said lower clad layer, (ii) a base formed fromsaid current block layer; and (iii) an emitter formed from saidsubstrate and said buffer layer.
 8. The device defined in claim 7wherein said pnp transistor part includes:a) said lower clad layer b)said current block layer c) said buffer layer and d) said substrate. 9.The device defined in claim 7, and including:a) a collector electrodeconnected to said lower clad layer; and b) a base electrode connected tosaid block layer.
 10. The device defined in claim 7, wherein the radiantpower is controlled by a small current injected from said baseelectrode.
 11. The semi-conductor light emission system as defined inclaim 7, the semi-conductor being constituted of a AlGaAs material. 12.The semi-conductor light emission system as described in claim 7, thesemi-conductor being constituted of a InGaAs material.
 13. Asemi-conductor light emission system having:a) a semi-conductor laserpart including:(i) a p-side electrode, (ii) a substrate (iii) a lowerclad layer, (iv) an active layer, (v) a first upper clad layer, (vi) acurrent block layer, (vii) a second upper clad layer, (viii) a contactlayer, (ix) a n-side electrode, and b) a pnp bi-polar transistor partconstituted in a position other than said semi-conductor laser part andincluding:(i) a base formed from said upper clad layer, (ii) a collectorformed from said current block layer, and (iii) an emitter formed fromsaid substrate and said lower clad layer.
 14. The device defined inclaim 13, and including:a) a base electrode connected to said upper cladlayer, and b) a collector electrode connected to said block layer, 15.The device defined in claim 14, wherein the radiant power is controlledby a small current injected from said base electrode.
 16. The devicedefined in claim 13, wherein said pnp bi-polar transistor partincludes:a) said lower clad layer, b) said active layer, c) said firstupper clad layer, and d) said block layer.
 17. The semi-conductor lightemission system as defined in claim 13, the semi-conductor beingconstituted of a AlGaAs material.
 18. The semi-conductor light emissionsystem as defined in claim 13, the semi-conductor being constituted ofan InGaAs material.
 19. A semi-conductor light emission system having:a)a semi-conductor laser part including:(i) a p-side electrode, (ii) asubstrate, (iii) a lower clad layer, (iv) an active layer, (v) a firstupper clad layer, (vi) a current block layer, (vii) a second upper cladlayer, (viii) a contact layer, (ix) an n-side electrode; and b) an npnbi-polar transistor part constituted in a position other than saidsemi-conductor laser part and including:(i) a base formed from saidcurrent block layer, (ii) a collector formed from said first upper cladlayer, (iii) an emitter formed from said contact layer.
 20. The devicedefined in claim 19, and further including:a) a base electrode connectedto said current block layer, and b) a collector electrode connected tosaid first upper clad layer.
 21. The device defined in claim 19, whereinsaid npn bi-polar transistor part includes:a) said first upper cladlayer, b) said current block layer, c) said second upper clad layer, andd) said contact layer.
 22. The semi-conductor light emission systemdefined in claim 19, the semi-conductor being constituted of an AlGaAsmaterial.
 23. The semi-conductor light emission system as defined inclaim 19, the semi-conductor being constituted of an InGaAs material.